Carrier transmission over power circuits



June l2, 1928.

R. K. HONAMAN CARRIER TRANSMISSION OVER POWER CIRCUITS Filed Oct. l5, 1924 @EWI NN x Ng L INVENTOR ZYam/aml@ swg y ATTORNEY Patented June 12, 1928.

UNITED STATES PATENT OFFICE.

RICHARD K. HONAMAN, F BLOOMFIELD, NEW JERSEY, ASSIGNOB TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK.

CARRIER TRANSMISSION OVER POWER CIRCUITS.

Application illed October 15, 1924. Serial No. 743,798.

'This invention relates to the use of power circuits for the transmission of signaling currents and more particularly to arrangements whereby carrier transmission channels l may be related to the conductors of a power system.

In accordance with the present invention, advantage is taken of the fact that current transformers, which are ordinarily associated l with a ,power system in order to step down 2 the circuits containing the current measuring device, relays, or other translatingv devices i through transformers which introduce very 0 is used for the other channel.

c w: eric low impedances into the circuits at ower frequencies. In order to obtain two signaling channels the transformers are so connected that one pair of the power conductors is used as a series metallic circuit for one channel, and a circuit consisting of the third conductor and the phantom of the first two Where different carrier frequencies are employed for transmitting in opposite directions thetwo channels may be used. one for transmitting in one direction and the other for transmitting inthe other direction to constitute a two-way signaling circuit. 'Where` however. the carrier apparatus is so arranged that signaling may take place in both directions on the same carrier frequency, the two channels may be used to carry on two two-way telephone conversations at the same time or, if desired. one channel may be used for carrying on a. telephone conversation and the other channel for auxiliary signaling.

The invention will now be more fully understood from the following description when read in connection with the accompanying drawing. the figures of which illustrate preferred embodiments of the invention. liteierring to the drawing, 1, 2 and 3 designate respectively three conductors of a well linown poli/phase type of power distribution systems. In order to measure the currentiiowing over the power distribution system it is customary to connect measuring instruments, such as 21, 22 and 23, in circuit with each of three conductors 31, 32 and 33, which are inductively related through current transformers 11, 12 and 13 with the three conductors 1, 2 and 3 respectively of the power distribution system. The transformers 11, 12 and 13 are transformers which step down the current flowing through the measuring instruments to values appropriate for indication by the measuring instruments.l The terminals of thel three measuring instruments are ordinarily connected together and grounded through a conductor of substantially no resistance. A t a distant point, similar current measuring apparatus may be provided, as indicated at the right-hand side of the figure, the various parts bein designated by the same numerals as have ay ready been referred to, the numerals, however, being primed.

In practice, the current transformers such as 11,k 12 and 13 have their windings constructed with relatively few turns so that the distributed capacity is very small, and although these transformers are primarily designed for the transmission of power frequencies such as currents in the nei hborhood of cycles, they are quite e cient transformers atthe much higher frequencies employedv in carrier transmission. Consequently, in superposing a carrier channel on a power distribution system it adds greatly to the economy of the system to be able to utilize the current. transformers for associating the carrier channel with the power conductors. JIn accordance with the present invention this result is accomplished'by connecting the winding 42 of a transformer between` the conductors 32 and 33, with a ground connection to the midpoint of the transformer, as shown. The other winding 43 of the transformer is connected in circuit with a channel leading to terminal carrier apparatus. the channel including the usual selective circuit, such as a filter TF. As a result of this connection the conductors 2 and 3 form the sides of a metallic transmission circuit, it being understood, of course, that similar transformer connections 42 and 43 are made at the. distant station.

An additional channel may be provided hy connecting the winding fi() of a transformer between the conductor 31 and the midpoint of winding L12, as shown, the secondary winding 41 being connected in the lib terminal circuit leading to carrier appara tus. The terminal circuit may include a selective device, such as a filter RF. A similar connection comprising transformer windings and il will, of course, be provided at the distant station.

It is essential that the introduction of the transformers in the current measuring circuits shall take place without substantially increasing the impedance at power frequencies. It may also be desirable, although not essential, to construct the transformers so that they are very ineflicient at low frequen-f cies while being quite' highly efficient at the higher frequencies.

If the transformer comprising windings 42 and 43 be carefully balanced with respect to ground. the crosstalk between the two channels afforded by the transformer connections shown will be reduced to a minimum and the requirements of frequency selectivity between the circuits will thereby be reduced. Signals may be transmitted` there fore, through the filter TF and the trans' former comprising windings 42 and 43 and thence over the conductors 2 and 3, forming a series metallic circuit to the receiving station. the signals being passed at the latter station through the transformer comprising windings 42 and 43 to the receiving carrier channel. Likewise, signals may be transmitted from the sending channel TF through the transformer comprising windings 40 and 4i'. The transmission path over the power conductors comprises in this lcase the power conductor l. with a return over the power conductors 2 and 3 in parallei. owing to the connection of one terminal of the winding fill to the midpoint of the winding 42. The signaling currents thus transmitted pass through the transformer comprising windings 40 and 4l and through the selective filter RF to the corresponding receivingn channel.

It will be readily understood that instead of using transformers 40-41 and 42-43 to couple the carrier channels to the current transformer circuit. the coupling may be e'ected through retard coils 40 and 42 connected as shown in Figure 2. These coils should. of course. be designed to meet the requirement of low impedance at power frequencies.

lt will be obvious that the general prin- -ciples herein disclosed may be embodied in -transformer having one winding serially connected between two of said local circuits and its other winding in a signaling circuit, a second transformer having one windin connected between the third local circuit an the midpoint of said first mentioned winding, the other windin of said second transformer being include in a second signalin circuit, said transformers being so designe that they introduce substant1al15Y no impedance at power frequencies.

2. In a three-wire power distribution system, a pair of stations interconnected through said three-wire system of conductors, current transformers at each station for individually connecting each wire of the three-wire conductor system to an individual local circuit, power translating devices in. said local circuits, means to establish a metallic signaling path over two of said conductors comprising a transformer at one of said stations having one windin serially connected between two of said loca circuits and its other winding connected to carrier signaling apparatus, a. transformer similarly connected at the other station, means for establishing a second signaling path utilizing the third power conductor and the phantom of the first two power conductors, said means comprising a. transformer at one station having a winding connecting the third local circuit to the midpoint of the winding of the transformer in the metallic circuit, the other winding of said transformer being in circuit with carrier signaling equipment. and means at the other station comprising a transformer similarly connected whereby signals may be inde endent-ly transmitted over the power con uctor system.

In testimony whereof. I havel signed my name to this specification this 14th day of October 1924.

RICHARD K. HONAMAN. 

